U.S. Pat. No. 4,094,777 discloses a process for the preparation of a mercury recovery mass comprising the incorporation of a copper compound with an inorganic carrier, followed by a sulfurization step at a temperature lower than 300.degree. C.
The sulfurization step of the process disclosed in this patent is performed by means of a gaseous agent, for example hydrogen sulfide, or of a solution of inorganic sulfide in water or in an organic solvent, for example an aqueous solution of sodium sulfide, potassium sulfide or ammonium sulfide.
The obtained masses have a high activity and are rather inexpensive. However, the preparation of said recovery masses suffers from several serious disadvantages.
For example, when the sulfurization is performed by means of gaseous hydrogen sulfide (H.sub.2 S), to obtain a recovery mass of sufficient activity, it is usually necessary to proceed at relatively high temperatures, for example example higher than 200.degree. C., which is disadvantageous. Moreover, H.sub.2 S is a toxic and malodorous product.
By using sulfur solutions, for example aqueous solutions of ammonium sulfide, it is possible to operate at a relatively low temperature, for example between 0.degree. and 100.degree. C. However ammonium sulfide is toxic and decomposes easily, which makes its use very difficult.
The mercury recovery efficiency of the masses obtained by this process decreases with time and their lifetime is limited.